1. Field of the Invention
The present invention relates to an optical recording medium such as an optical disc, a recording apparatus for the optical recording medium, a recording/reproduction apparatus, a recording method, and a recording/reproduction method.
2. Description of the Related Art
Data recording/reproduction techniques are known which use optical discs as recording media, such as CDs (Compact Discs) and DVDs (Digital Versatile Discs), for recording/reproducing digital data. The term “optical discs” refers in general to recording media formed of a thin circular metal plate protected with plastic, onto which laser light is irradiated so that a data signal can be read by detecting variations in the intensity of reflected light.
Optical discs include, for example, reproduction-only type-optical discs, such as CDs, CD-ROMs and DVD-ROMs, and recordable-type optical discs, such as MDs (Mini-Discs), CD-Rs, CD-RWs, DVD-R, DVD-RWs, DVD+RWs, and DVD-RAMs in which user data can be recorded. Data can be recorded on such recordable-type optical discs by employing recording techniques such as magneto-optical recording, phase-change recording, and dye-film change recording. Dye-film change recording is also called write-once recording and is preferable for a data storage application, since it permits recording of data only one time and does not permit rewriting of recorded data. In magneto-optical recording and phase-change recording, on the other hand, rewriting of data is permitted. Thus, these recording techniques are used for various applications such as recording of content data of music, movies, games, application programs, etc.
In recent years, a high-density optical disc called Blue-ray Disc has been developed with a view to realizing a significant increase in capacity.
In such a high-density optical disc, for example, when recording/reproduction is performed using a laser with a wavelength of 405 nm (i.e., a blue laser) and an objective lens with an NA of 0.85, approximately 23.3 GB (gigabyte) of data can be recorded on or reproduced from a disc having a diameter of 12 cm. In this example, this large capacity is achieved when the disc has a track pitch of 0.32 μm, a linear density of 0.12 μm/bit, and a format efficiency of 82% with a recording/reproduction unit of a 64 KB (kilobyte) data block.
Further, if the linear density of the above optical disc is 0.112 μm/bit, a 25 GB capacity can be achieved.
Moreover, by adding a further recording layer so that the optical disc has two recording layers, the capacity can be doubled to 46.6 GB or 50 GB.
Needless to say, by increasing the number of the recording layer to three, four, . . . N, a capacity of 23.3 GB or 25 GB times three, four, . . . N can be realized.
The write-once type and the writable type of such high-density optical discs have also been developed.